Double sickle or split sickle mowing devices such as shown in U.S. Pat. No. 3,577,716, issued to Horace G. McCarty, et al on May 4, 1971, have proved to be particularly advantageous on harvesting machines having a relatively wide cutting width, at least in part due to the counter reciprocating masses of the opposing sickles. A relatively recent innovation in the marketing of reciprocating cutterbars has been the utilization of easily removable threaded fasteners to connect the individual sickle sections to the support bar running transversely along the cutterbar, as shown in U.S. Pat. No. 4,198,803. Prior to the utilization of these threaded fasteners, knife sections were typically riveted to the support bar.
As can be seen in the aforementioned U.S. Pat. No. 3,577,716, this split sickle-type of cutterbar provides for an overlap of the individual sickles at the transverse center of the harvesting machine. In this overlap area, the overlapping knife sections move in close proximity to each other and can actually sever crop by shearing against each other, as well as against the knife guards, during their operative movement. This close proximate relationship requires that the fastener, e.g. rivet, not have a head protruding outwardly beyond the surface of the knife sections facing the opposing knife section against which the shearing relationship exists.
A combination of the teachings of the split sickle device taught in the aforementioned U.S. Pat. No. 3,577,716 and the teachings of the aforementioned U.S. Pat. No. 4,198,803, in which the rivets had been replaced by threaded fasteners, has resulted in double sickle cutterbars having threaded fasteners attaching the knife sections to the respective support bars along the entire width of the cutterbar except in the overlap area where conventional riveting has been utilized because an effective threaded fastener system has not been developed. Accordingly, it would be advantageous to provide a threaded fastener that could be used in conjunction with double sickle cutterbars in the overlap area to gain the advantages associated with the easy removal of knife sections attached to the corresponding support bar by threaded fasteners along the entire length of the cutterbar, thereby providing an improved double sickle cutterbar.